The SMART CUT® process allows the transfer of a thin semiconductor layer from a donor substrate to a receiver substrate and applies the following steps:                a) Implanting atomic species in the donor substrate to create a weakened zone, the depth of which corresponds to the thickness of the thin layer it is desired to transfer.        b) Contacting the substrates and bonding via molecular bonding.        
Bonding occurs over the entire surface of the substrates except on the periphery since the wafers have an Edge Roll Off (ERO) and are, therefore, not in contact on their periphery as can be seen in FIG. 1.                c) Detaching along the weakened zone of the donor substrate, and transfer of the thin layer onto the receiver substrate.        
Substrates are generally in the form of circular wafers; e.g., wafers of 300 mm are commonly used.
The peripheral region where transfer of the thin layer does not take place is known as a “crown.” With reference to FIG. 2 illustrating an overhead view of four peripheral regions of an SeOI wafer, the crown CP is delimited on the outer side by the edge 100 of the receiver substrate and on the inner side by the edge 200 of the transferred layer. The wafer in FIG. 2 has a regular crown CP, in other words, the edge of the SeOI is regular.
However, in some cases, a jagged edge is obtained on the end product, i.e., the SeOI obtained after detachment. After detachment, it can occur that the crown also comprises small, isolated transferred zones.
The width of the crown is, therefore, made jagged through the local, uncontrolled extension of the transferred region over several hundred micrometers, toward the edge of the receiver substrate. The extension of the transferred region can be seen in the photos in FIG. 3 where the lightest region corresponds to the transferred layer and the darkest layer is the crown.
One situation in which a jagged crown is observed is when the surface of at least one of the substrates is activated before molecular bonding, e.g., via plasma activation. This activation allows significant reinforcing of bonding energy. The reinforcing of bonding energy can also be obtained by adapted cleaning before bonding, e.g., a sequence of O3/SC1/SC2 type where SC1 is conducted at a temperature lower than 50° C.
Patent application WO 2009/034113 by the Applicant proposes overcoming this disadvantage by controlling activation of the surface of the substrate so that the increase in bonding energy between the donor substrate and receiver substrate, in a peripheral region of these substrates, is lower than the increase in bonding energy in the central region of the substrates.
However, situations subsist in which the jagged edge phenomenon is still observed, even when the abovementioned controlling is applied. These are, in particular, cases in which the transferred semiconductor layer is of a large thickness, i.e., typically greater than or equal to 370 nm, and in which the weakened zone is formed by co-implantation of two different species, generally hydrogen and helium.
Yet this undesired transfer into the crown creates a weaker zone in which the transferred semiconductor layer is likely to undergo chemical attack through its interface with the receiver substrate (phenomenon known as “under etching”) and will delaminate.
One solution to overcome this type of defect would be to remove the zones transferred into the crown via mechanical or chemical action.
However, the performing of such corrective operations would be complicated to implement on an industrial scale and would impact the manufacturing cost of SeOI structures.